Intraoperative autotransfusion system (IOAT) aspirates waste blood from surgical wound site, purifies and returns it to the same patient. We developed and evaluated in-vivo a new IOAT system which is designed to purify the aspirated waste blood using hollow fiber membrane ultrafilter/plasma filters instead of using centrifuges, and return the purified whole blood to the patient in a closed loop continuous on line operation within a few minutes without significant wastage of blood cells and clotting factors. Preliminary in-vivo evaluations of our Membrane Autotransfusion System (MATS) during implantation of artificial ventricles in calves have lead us to redefine the design parameters. We rebuilt our MATS so that it could respond to the rapidly changing operating conditions, such as blood flow rate (o to 2,000 ml/min, hematocrit (o to 45%), air emboli & froth, macroaggregates, irrigating fluid, shear rate, transmembrane pressure, duration of operation, and systemic heparinization. Phase-I involves extensive in-vivo studies using calf and human blood with an objective to establish the consistency of performance of the system in response to the rapid changes in operating conditions. Phase- II involves evaluations (i) during total artificial heart implantation studies in calves, and (ii) in ten calves, where bleeding will be simulated in open chest cavity, and the shed blood will be salvaged by our membrane autotransfusion system. Total available market is expected to be over $120,000,000 in the U.S. There is a strong need for this device in view of the present scare in donor blood transfusions related to transmission of AIDS and hepatitis.